Drupal ajax form submit progress overlay

Use below code to show progress bar while submitting ajax form in Drupal.

/* ajax form submit throbber style */ 
.custom_wrap .ajax-progress .message,
.custom_wrap .ajax-progress-throbber .message{
  color: white;
  font-size: 20px;
  padding: 30px;
}
.custom_wrap .ajax-progress .throbber,
.custom_wrap .ajax-progress-throbber .throbber {
  float: none;
  margin: 250px auto 0 auto;
  width: 128px;
  height: 128px;
  background: url("../images/ajax-throbber.gif") no-repeat center center;
}
.custom_wrap .ajax-progress,
.custom_wrap .ajax-progress-throbber {
  width: 100%;
  height: 100%;
  background-color: #000;
 opacity: 0.6;
 filter: alpha(opacity=60);
  position: fixed;
  top: 0;
  left: 0;
  z-index: 500;
  vertical-align: middle;
  text-align: center;
}